There are many applications in which dyes, including infrared light absorbing compositions, when dissolved or dispersed in a host liquid, solid or gel, provide light absorption and, in some cases, fluorescent or phosphorescent light emission. For example, non-luminescent or weakly luminescent infrared compositions are used in light filters. Luminescence encompasses all light emission whether by fluorescence, phosphorescence, or an undetermined emission mechanism. Such infrared light filters are utilized in sensors, including solid state detectors, photodiode arrays, imaging (camera) sensors (charge-coupled devices (CCD) and complementary metal oxide semiconductor (CMOS)), and other devices, to shape the sensitivity curve of a broadly photosensitive element(s), for example, by absorbing invisible light to provide a responsivity curve similar to that of the eye. Filters including such infrared absorbing compositions are also used to protect sensors or the eye from infrared radiation, for example, laser radiation or other sources of infrared light, such as welding operations or arc flash. Infrared wavelength filters may also be used to diminish the intensity of the infrared light energy emitted from natural or artificial illumination sources, from information displays, including CRTs, liquid crystal and plasma displays, light emitting diodes, and other emissive technologies such as organic light-emitting diodes (OLEDs), especially in cases where such infrared light sources may interfere with the operation of infrared sensors. Infrared absorbing compositions may also be used to provide infrared blocking in otherwise infrared transparent or partially infrared transparent plastic articles, e.g., banking or credit cards, in which visibly partially transparent plastics provide for marketing or security features. Infrared absorbing compositions may also be used in cell biology applications, in inks or in heat activated compositions.
Infrared absorbing compositions have a long history and thousands are known. Infrared absorbing compositions may also be categorized into several other classes of chemical compounds including, among others, polymethine dyes, the phthalocyanines and their metal complexes, naphthalocyanines and their metal complexes, anthraquinone derivatives, rylenes, dithiolenes (also known as metal complex dyes), aminium salts, and diimmonium salts. Polymethines and unsubstituted phthalocyanines and naphthalocyanines have relatively narrower absorption bands than dithiolenes, anthraquinone derivatives, aminium salts or diimmonium salts. Both narrow and broad band absorbing compositions are useful because each has performance advantages in certain applications.
The first report of the spectral properties of infrared light absorbing aminium dyes was by Neunhoeffer et al., Chemische Berichte 92, 245-251 (1959). Subsequent development of these dyes at American Cyanamide by Milionis, Susi et al. has been reported in the patent literature, e.g., U.S. Pat. No. 3,341,464,“Heat Resistant Aminium Salt Infrared Absorbers” issued Sep. 12, 1967; U.S. Pat. No. 3,400,156, “Triaminotriphenylaminium Salts” issued Sep. 3, 1968; U.S. Pat. No. 3,440,257, “Tris(p-Dialkylaminophenyl) aminium Hexafluoroantimonates and -Arsenates” issued Aug. 22, 1969; U.S. Pat. No. 3,484,467, “Diaryl-(N,N-Diarylaminoaryl)-Aminium Hexafluoroantimonates and Hexafluoro-arsenates” issued Dec. 16, 1969; U.S. Pat. No. 3,575,871, “Tetraaryl Arylaminium Salts and Use as Infrared Absorbers” issued Apr. 20, 1971; and U.S. Pat. No. 3,631,147, “Preparation of Monocation Salts of N,N,N′,N′-Tetrakis(p-Dialkyl Aminophenyl)-p-Phenylene-diamines” issued Dec. 28, 1971. Various other patents teach methods of preparation of intermediates and the use of such aminium salts as infrared absorbing components of light filters.
The limited thermal stability of many aminium and related diimmonium salts was immediately recognized. Studies showed that the hexafluoroantimonate (SbF6−) and, to a somewhat lesser degree, hexafluoroarsenate (AsF6−) salts of the aminium ions were the most heat resistant. Such work was extended by Cahill, et al., U.S. Pat. No. 7,498,123, with the use of non-coordinating ions such as (C6F5)4B—. Therefore, it is not surprising that the most thermally stable salts of both the aminium and diimmonium chromophores have been widely used as infrared absorbing components in light filters. The diimmonium compositions tend to be less thermally stable than the aminium compositions, and may undergo reduction at elevated temperatures to give the corresponding aminium salt.
One of the most desirable resins or polymers for use in light filters is polycarbonate. Polycarbonate, also frequently referred to by its various trade names, Lexan®, Calibre®, Iupilon®, Makrolon®, etc., can be formulated and molded at high pressure into various shapes in a high temperature process. Polycarbonate's combination of optical and mechanical properties often makes this resin the polymer of choice for ophthalmic and ballistic uses, as well as other applications.
A limiting aspect to the utility of current aminium compositions, particularly in applications such as laser eye protection in which high optical densities are often required for protection against Nd:YAG, Nd:glass, and other laser wavelengths from about 1050 to 1100 nm, is the relatively short peak wavelength of the (4-R2N—C6H4)3N+.absorption band near 1000 nm.
Another limiting aspect to the utility of current aminium compositions, particularly in applications such as security or authentication in which low visible color in printing, coating, or mass dyeing is required, is the distinct green color of the (4-R2N—C6H4)3N+.chromophore. The green color of the compositions originates from a combination of an absorption band at blue-violet wavelengths and the absorption due to the tail of the infrared absorption band at red wavelengths.
One path to a solution to the fabrication of light filters with improved light absorption at wavelengths of about 1050 to 1100 nm is to shift the peak wavelength of the aminium dye to longer wavelengths, for example, by increasing the electron donating power of the groups attached to the peripheral nitrogens. However, this approach may be detrimental to the overall performance of the light filter because, by this approach, the blue-violet absorption band of the chromophore may shift to longer wavelengths, possibly decreasing the visible light transmission of the filter.
Accordingly, there is a need for long-wavelength infrared light absorbing compositions that overcome one or more of the aforementioned drawbacks of current compositions. There is also a need to provide light filters using such compositions that are capable of filtering out undesirable, harmful, or dangerous wavelengths of infrared light. There is also a need to provide light filters comprised of plastic resins that have desirable levels of apparent color and infrared absorption. In addition, there is also a need to provide light filters in thin cross-sections or films where highly soluble dyes are required to reach high optical densities, especially in low polarity hosts, for example, hydrocarbons and hydrocarbon polymers, silicones, partially fluorinated liquids or polymers, or other solids, liquids, or gels, or in thin films.